Desulfurization process using alkali followed by extraction with liquid sulfur dioxide and a promoter



H 9 M 8 w A". S 4 2D E 6 w 7 wm ww 6 MU HW R 5 H F O Tn" Fm n y 3 f mLf/ l .m 5 u M w nf msm mm L 1 0 DAwww a w w LnNuwml 2 5 I mmre, l :4J RMAY f AIDM A .EWMJ :./v CNEd .RODS H RPNTI. 0 NOX 7 AO C mRI 3 TTD ...ALAVA .f7 6 ZE s? on 2 3 I /y 4 2 lli 3 F fav 8 2 L 2 9 R Ww 2 E 4 E YJ 3v/A l 3 D 4 anun M 2 HN b f wm 7 2 S d May 8, 1956 WML/M .w31 m MA V.. 70 m w. n/O 6 6 4, m Am 2 H a M Y m d m m w /F n W m m m E wm 3 P 9 9 6 9m f w M utkm. @02W 7 8 7 B Y r .f 4 s M R/ 7/ JWM UW 27u D pn. 5 m m w HG 6 E2 x 2 oo 7 0 8 ha M :u/ 54 8 8 f 0^ L 6 ATTORNEY United StatesPatent O DESULFURIZATION PROCESS USING ALKALI FOLLOWED BY EXTRACTIONWITH LIQUID SULFUR DIOXIDE AND A PROMOTER Robert C. Arnold, Park.Forest, Ill., assigner to Standard Oil Company, Chicago, Ill., acorporation-of Indiana Application July 9, 1953, Serial No. 366,957

Claims. (Cl. 196-32) This invention relates to a process for refininghydrocarbon materials containing one or more undesired impurities, suchas coloring matter,.rnalodorous materials and organo-sulfur compounds.More particularly, this invention is concerned with'a process fordesulfurizing mercaptan and other organo-sulfur compound containinghydrocarbon oils, particularly sour petroleum' oil distillates boilingin the heavier-than-gasoline range.

Patent application Serial Number 248,898, iiled September 29, 1951, nowPatent No. 2,671,047, entitled Refining Hydrocarbon Materials with SO2and BFa by Robert C. Arnold and Arthur P. Lien discloses a process fordesulfurizing organo-sulfur compound containing hydrocarbon materials bythe treatment thereof with an agent consisting essentially of liquid SO2and BFa. This process gives a markedly greater amount of desulfurizationthan does an equivalent amount of liquid SO2 alone. Also, thisprocessconverts a sour, i. e., mercaptan containing, oil into an oilthat is sweet to the doctor test. These improved results are obtainedwith substantially no increase in the amount of hydrocarbons taken intothe extract phase. However, it has been found that the raflinate oilfrom this process, although of markedly lower organo-sulfur compoundcontent, contains appreciable amounts of elemental sulfur. The elementalsulfur is present in the raffinate oil even though none had been presentin the sour oil feed to the process. The presence of elemental sulfur inhydrocarbon oils such as naphthas, kerosenes, vheater oils, or highsolvency naphthas has an extremely bad effect on product quality asdetermined by the copper strip method.

One object of the present invention is to provide a process for reningand desulfurizing hydrocarbon oils containing organo-sulfur compounds.An additional object is to providel a process for decolorizinghydrocarbon materials, particularly hydrocarbon oils. A specic object ofthe invention is to provide a process for the treatment of a petroleumdistillate containing objectionable amounts of organo-sulfur compoundsto produce a product oil of low organo-sulfur compound content and alsoessentially free of elemental sulfur. These and other objects of theinvention will become apparent from the following description. l

It has been discovered that elemental sulfur is not present in theproduct of the treatment of hydrocarbon material containingorgano-sulfur'compounds with an agent consisting essentially of liquidSO2 and a promoter selected from the class of Lewis acids(Friedel-Crafts halides) when the hydrocarbon oil is treated tosubstantially eliminate mercaptans prior to undergoing the liquidSO2-promoter treatment. Thus the process of this invention comprises (l)treating a hydrocarbon material containing mercaptans and otherorgano-sulfur compounds to substantially eliminate the mercaptans,either by physical removal or conversion to the correspondingdisuliides. (2) Contacting said substantially mercaptan-free oil with anagent consisting-essentially of liquid SO2 and ,a promoter selected fromthe class of Friedel-Crafts lcg halides consisting of BFa, AlCla, FeCls,TiCl4, HgClz, BCla and ZnClz. At least enough liquid SO2 is present inthe agent to exceed the solubility of liquid SO2 in the oil undergoingtreatment. The temperature of the treatment is below about 10 C. (3) Araiiinate oil of markedly lower organo-sulfur compound content andessentially free of elemental sulfur is separated from an extract phasecomprising agent, sulfur compounds and extract hydrocarbons.

The SO2-promoter process is applicable to various liquid or liquefiedhydrocarbon materials which contain organo-sulfur compounds. Thus it isapplicable to various petroleum fractions for the purposes of removingsulfur, gums or other resinous materials, colored impurities andodoriferous compounds. feed stocks may comprise light naphtha fractions,gasolines, heavy naphthas, kerosenes, transformer oils, heater oils,furnace oils, diesel fuels, gas oils, lube oils and crude oils.Particularly suitable charging stocks are petroleum distillates boilingin the heaVier-than-gasoline range, i. e., between about 330 and 675 F.

This process can be applied for the purpose of desulfurizing variouspetroleum stocks which are to be subsequently treated .in refining yorconversion operations ,in which sulfur or sulfur compounds areundesirable, for example, catalytic cracking operations, catalyticreforming operations, catalytic hydrogenation in the presence ofsulfur-sensitive catalysts and the like.

In addition the refining agents of the present inven-y y tion may beapplied to the desulfurization and decolorization of aromatichydrocarbon fractions, for example, crude ben'zols, toluols, xylols,naphthalene fractions'or the like. r

VThe process may also be applied to the refining of various coal tarfractions and coal tar distillates. In the refining of shale oilfractions the refining agentsserve not only to remove organic sulfurcompounds from the feed stock, but also to remove oxygen compounds andnitrogen compounds. v

It is to be understood that the above specific examples of chargingstocks which may be refined by the present invention are illustrativeonly and are not intended to limit the field of applicability of theprocess.

Any method which produces a substantially sweet oil may be utilized inthe process of this invention. Although the mechanism is not understood,the mercaptans present in the feed oil appear to be the cause of theformation of elemental sulfur in the SO2-promoter process. A product oilthat is free of elemental sulfur can be obtained if the mercaptans areeliminated from vthe oil.v

Any conventional process for the physical removal of mercaptans may beutilized, e. g., the sour oil may be contacted with an aqueouscaustic-organic solvent solution. The organic solvent may be amonohydric alcohol ksuch as methanol or ethanol; a dihydric alcohol suchas ethylene glycol; or a dihydric alcohol containing ether linkages suchas diethylene glycol or triethylene glycol, Other organic solvents suchas water-soluble aliphatic amines or alkanolamines may be used. Thevarious soluti'zer processes may be used. In these processes thesolution consists of aqueous caustic and a solubility promoter such asphenolic compounds, lower molecular weight fatty acids, wood tar oils,and tannins;

yAny conventional process for the Aconversion of the mercaptans to thecorresponding disuliides wherein .the disuldes are dissolved in the oilmay be used. Examples of these processes are: Contacting the sour oilwith concentrated aqueous caustic solution in the presence of.free-oxygen. Contacting the' sour oil' with aqueous caustic solution,free-oxygenand catalysts for vthe oxidation of mercaptans such ashydroquinone, pyrogallol,

Suitable petroleum tannin, petroleum phenols, etc. Contact-ing the souroil with concentrated aqueous caustic solution and freeoxygen in thepresence of active copper catalysts such as CuSO4 and CuClz.

The most widely used processes for sweetening sour oils Vby theconversion of mercaptans to disuliides are the doctor process and thecopper chloride process. ln the doctor process the sour oil is contactedwith an aqueous caustic solution containing dissolved litharge andfree-oxygen in the presence of elemental sulfur. In the copper chlorideprocess the sour oil is contacted with free-oxygen in the presence of acatalyst mass consisting essentially of copper chloride, water and aninert support.

It is to be understood that any process which results in the productionof a substantially sweet oil may be utilized and the process of thisinvention is not limited to the processes listed above.

In general, the proportion of liquid sulfur dioxide used variesdepending upon vthe specific hydrocarbon material being treated. and thetreating conditions, especially the temperature. The relativeiniscibility of liquid sulfur dioxide and hydrocarbon charging stocksvaries with temperature, greater' mutual miscibilities being encounteredat higher temperatures and lower miscibilities at lower temperatures. Atleast a suiicient amount of sulfur dioxide is used to exceed itssolubility in the hydrocarbon material being treated at the particulartreating temperature, thereby forming two distinct liquid phases, i. e.,a predominantly hydrocarbon liquid phase containing a relatively smallproportion of dissolved sulfur dioxide or raffinate layer and apredominantly sulfur dioxide liquid phase or extract layer. Ordinarily,liquid sulfur dioxide is employed in the process in amounts betweenabout percent and about 200 percent by volume or more, based on thevolume of hydrocarbon charging stock. Preferably, between about and 75volume percent of liquid SO2 is used.

,The sulfur-removing powers of liquid SO2 are remarkably` enhanced bythe addition thereto of a promoter selected from the class of Lewisacids (Friedel-.Crafts-type halides). Not all the .members of the classof compounds known as the Friedel-Crafts-type halides can be used inthis process. Some members are completely ineffective, for example,aluminum triuoride, or are only feebly eective, for example, antimonytrichloride, aluminum bromide and stannic chloride. A high degree ofsolubility in the liquid SO2 is helpful. However, some members of lowsolubility are good promoters when used in the form of a liquidSO2-promoter slurry, for example, FeCls, HgClz, and ZnClz. The membersof the class which are eifective as sulfur removal promoters in liquidSO2 extraction are AlCls, FeCla, TiCl4, BFs, HgCla, BC13, and ZnClz.With the exception of .BFg these promoters do not appear to givecomplete sweetening when a sour oil is contacted with the v.SO2-promoteragent. However, a suicient amount of sweetening occurs with all thepromoters to produce a deleterious amount of elemental sulfur in theproduct oil if the sour oil is not sweetened prior to contacting withthe SO2-promoter agent. Because of its solubility in liquid SO2, ease inrecovery from the extract phase and superior desulfurization obtainedtherewith, BF3 is preferred.

The amount of promoter employed in the process will usually vfall withinthe range of about 0.5 to about 5 mols per gram atom of sulfur containedin the hydrocarbon charging stock. The proportions of promoter to sulfurwithin the above range, when employed with liquid sulfur dioxide, aresufficient not only to eiect substantial desulfurization ofsulfur-,containing hydrocarbon materials but also to effect additionalrefining, particularly decolorization. For purposes of desulfurizationit has been discovered that the optimum desulfurization can be eiectedby the employment of between about 1 and about 3 mols of promoter pergram atom of sulfur contained in the hydrocarbon charging stock. (It isto bc understood that at least a suicient amount of liquid sulfurdioxide to form a liquid phase distinct from the raffinate hydrocarbonmaterial is also present in the contacting zone.)

The SO2-promoter process may be conducted at temperatures between about-l-l0 C. and 85 C. The preferred temperature range is between about 10C. and -40 C. The optimum temperature will vary not only with the typeof charging stock but also with the desired product, i. e., maximumdesulfurization and maximum color improvement may require differenttemperatures at otherwise constant conditions of operation.

The SO2-promoter process is conducted under pressure suicient at leastto maintain a substantial proportion of the sulfur dioxide in the liquidstate and likewise sufficient at least to maintain a substantialproportion of the gaseous promoters dissolved in the liquid phase. Inthe presence of liquid sulfur dioxide, BF3 forms extremely stableaddition compounds with organo-sulfur compounds and, as a result, asubstantial proportion of BFs which is originally introduced into thereiining zone as a gas is rapidly absorbed. The partial pressure of BFSin equilibrium with said BFS-sulfur compound addition compounds is verylow at temperatures of 0 C. or less. In general, the SO2-promoterprocess can be operated at pressures which are commonly encountered incommercial process equipment, for example, between about l and about 300p. s. i. g., although usually pressures between about l and about 15 p.s. i. g. are suiicient for the present purposes.

The contacting time required in the SO2-promoter process is dependentupon the intimacy of contacting with the refining agent of thehydrocarbon material being treated and upon the operating temperature.Ordinarily, the .contacting time may be between about l and 60 minutes.The operating temperature will, to some extent, aifect the intimacy ofcontacting by determining the liquid viscosities in the refining systemand, probably to a more important extent, by determining the rate ofinteraction of sulfur compounds and other impurities in the feed stockwith the refining agent.

Various diluents, countersolvents or co-solvents can be employed in thepresent process in addition to the refining agent. Especially in thecase of viscous or relative high pour point hydrocarbon charging stocksit may be desirable to dilute said charging stocks with diluents orcountersolvents such as liquefied propane, .butanes, pentanes, hexanes,saturated naphthas or the like. The use of Various co-solvents,particularly benzol with liquid sulfur dioxide, is well-known and theseco-solvents may find application in the process.

It is possibleto heat the total extract phase from the process untilsubstantially all the SO2 has been vaporized off without substantiallydecomposing the prornoter-sulfur compound adduct, lif the temperature ofthe extract phase does not exceed about 50 C. When using BF3 as thepromoter, the free BF2., i. e., the BF3 existing insimple solution inthe extract phase, passes off along with the gaseous SO2. Partialremoval of the SO2 results in the separation of a second ralinate layerand the yield of the second raiiinate .reaches a maximum whensubstantially all the SO2 has been removed. When substantially all theSO2 has been removed from the first extract phase, the secondrailinate-consists essentially of all the aromatic hydrocarbonsextracted from the feed stock and some sulfur compounds, as evidenced bythe sulfur kcontent thereof; and the second extract phase consistssubstantially of an adduct of promoter and sulfur compounds. Theamountof SO2 present in the second extract phase may vary from about l toabout l5 volume percent depending upon the temperature at which the irstextract phase was heated in order to remove SO2 and free BF3. The sulfurcontent of the aromatic hydrocarbon containing second raiiinate obtainedby lthis SO2 removal technique is less than lthe sulfur contentvof ithetotal extract materials; and may be in some cases as low as 0.1 weightpercent.

When the extract phase is treated so as'to remove substantially all theSO2, the second extract material appears to consist essentially oforgano-sulfur compounds. Treatment of a West Texas heater oil containing0.6 Weight percent sulfur with 2 mols of BF3 per mol of sulfur dissolvedin 25 volume percent of liquidv SO2, separation of the resultant extractphase, removal of the SO2 and free BFa from the extract phase at about25 C. gave a second extract material with a sulfur content of 12.1%. Thesecond raflinate consisted of aromatic hydrocarbons and enoughorgano-sulfur compounds to give a sulfur v content of 4%.

The SO2-promoter process can be carried out in batch, continuous orsemi-continuous operating cycles, and-in one or more stages, employingcontacting and separation equipment such as has heretofore been employedin the selective solvent refining of petroleum lubricating oil stocks orin effecting the alkylation of isoparatiinic hydrocarbons with oleiinsin the presence of liquidacid catalysts. It should be understood thatthe -speciiic equipment employed forms no part of the present inventionand that any equipment ladaptable for the purposes of contacting therefining agent with the hydrocarbon charging stock and thereafterseparating spent refining agent from the rened charging stock can beemployed for the purposes of the invention.

The invention is illustrated by one embodiment shown in the annexeddrawing which forms a part of this specification. Numerous pumps, valvesand other items of equipment have been omitted from this embodimentsince these items may be Vreadily added thereto by those skilled in theart. l

The feed stock to the process is a heater oil derivedby distillationfrom West Texas crude. This feed boils be-v tween 375 and 560 F. and hasa mercaptan number of 90. Since this feed is to be sweetened by thelcopper chloride process, itshould be Has-free. The H2S has been removedby Washing with a dilute aqueous caustic solution. Other methods ofremoving Has may beiused. (Some sweetening methods do not requireremoval of the Has).

Caustic reacts with the copper catalyst and deactivates it. Therefore,it is necessary to remove any caustic which may be present in the feed.Thesour oil feed in this illustration is passed from source 11 throughline 12 into salt iilter 13. Salt filter 13 consists of a cylindricalvessel filled with crushed rock salt. The rock salt removes any aqueouscaustic that may be occluded, in the feed. Instead of using a salt drum,a vessel filled with steel wool, gravel, sand or other coalescing mediummay be used.

The feed is passed out of salt lter 13, through line 14, into heatexchanger 16. In heat exchanger 16 the temperature of the sour oil israised to about 80 F. In general, the temperature of operation should bebetween about 60 and 100 F. From heat exchanger 16 the sour oil ispassed by way of line 17 into mixer 18. Mixer 18 may be any form ofagitating device. In this case mixer 18 is provided with knotholeorifice plates. Freeoxygen from source 21 is passed through line 22 intoline 17 where it meets the main stream of sour oil. The free-oxygen andthe sour oil 'are thoroughly intermingled in mixer 18.

Theoretically, the amount of free-oxygen needed in the process to insuresubstantially complete regeneration of the catalyst is 1 mol for each 4mols of mercaptan present. However, normally a 100 or 200% excess isdesirable.

A side stream of the sour oil is withdrawn from line 17 by way of line24 and is passed into slurry tank 26. Slurry tank 26-is a cone-bottomedvessel provided with anagitator not shown. Fresh catalyst from source 27or ammonium chloride.

is added by way of line 28 to slurry tank 26. The slurry of catalyst andoil is passed from tank l26 throughline 29 by way of pump 31 into line32. The mainstream of sour oil is passed from mixer 18 by way of line 34and pump 36 into line 37 where it meets the makeup catalyst slurry fromline 32.

The catalyst comprises CuClz, water and a carrier. The carrier consistsessentially of a nely powdered mixture, having a screen size of lessthan about mesh of fullers earth. Adsorbed on the carrier is an aqueoussolution of CuClz. Based on the total catalyst, the catalyst shouldcontain between about 5 and 30 weight percent of waterand between aboutl and 25 weight percent of CuClz. (However, the v CuClz may be' made byreacting in aqueous solution cupric sulfate and sodium chloride Whenforming the CuClz'by this reaction, it is preferred to use a smallexcess of the chloride salt.) f

The sour oil-oxygen-catalyst dispersion in-line 37 is passed intoeductor 38 and from eductor 38 it is passed through line 39 into reactor41. In some cases the eductor may be by-passed and the dispersion passedinto line 39 by way of by-pass line 42. In reactor 41 the sour oilandthe catalyst are maintained in the dispersed condition until the oilis substantially sweet.

Reactor 41 has a conical shaped lower portion into which the catalystsettles. The dense slurry of catalyst and oil is withdrawn from thebottom of reactor 41 through line 46 and is passed into eductor 38 byway of line 47. ln Veductor 38 the recycle catalyst meets the stream ofsour oil and makeup catalyst.` When the catalyst has becomesubstantially inactive, catalyst is sent to recovery by way .of lines 46and 49.

The substantially sweet oil contains a very slight amount of catalyst.The oil is withdrawn from reactor 41 through line 51 and is passed intoline 52 wherev it meets water from source 53 and line 54. The amount ofwash water used is dependent upon the amount of catalyst carried overfrom the reactor. In general, the amount of wash water may be betweenabout 10 and 100 volume percent based on oil. The mixed stream of waterand oil is passed into mixer 56. From mixer 56 the stream of oil andwater is passed by way of line 57 into settler 58. The wash waterseparates in settler 58 and is sent to a sewer by way of line 59. Thewashed oil from settler 58 is passed into line 61. In some cases thewashing operation is not necessary and the operation may be' bypassed byway of lines 51 and 62.

The washed oil from line 61v is passed through line 63, through cooler64 and line 66 into salt tilter 67. Cooler 64 lowers the temperature ofthe washed oil in order to reduce the amount of water dissolved in theoil, and salt lter 67 dehydrates the washed oil. Brine from vessel 67 ispassed to the sewer by way of line 68.l Salt filter 67 is similar inconstruction to salt lter 13.

Dehydrator 67 may comprise other conventional equip-I ment and dryingreagents, for example, a vessel packed with calcium chloride, excelsior,fiber glass, magnesium silicate drying agents (Florisil), alumina gel orthe like. Drying of the oil can also be effected by distillation, forexample, vacuum distillation.

It should be understood that the specic vdrying treatment forms no partof the present invention and that any drying treatment may be used whichsubstantially eliminates Water from the charging stock. The presence ofwater in the charging stock and in the treating system is extremelyundesirable since water combines with BFs to form hydrates, whichcomplicates the recovery of BFs, and since the corrosive tendencies ofthe" SO2-promoter agent tend to increase with increasing waterconcentration in the refining system.

The dried oil is passed through line 69 into deaeration equipment 71wherein air dissolved incr entrained in the charging stockis,substantially removed. The specific deaeration process and equipmentform no part of the 7 present invention. Vacuum deaeration equipmentsuch as is ordinarily employed in commercial processes of liquid sulfurdioxideireiining of hydrocarbon oils can be employed. The deaerated oilis passed through line 72 into heat exchanger 73 wherein the temperatureof the stock is lowered to the desired treating temperature.

The oil thus pretreated is introduced by way of line 7 into the lowerportion of extraction tower 76. The extraction tower may be packed withsuitable corrosionresistant packing materials to increase the efficiencyof contacting of the charging stock and reiining agents. For example,the extraction tower can be packed with structural carbon in the form ofBerl saddles, glass or porcelain spheres, Monel metal fragments, mildcarbon steel jack chain o r the like, or may be provided withmechanically- 'or magnetically-actuated agitators.

If desired, ythe viscosity of the hydrocarbon charging stock may bereduced by dilution with a saturated hydrocarbon such as n-pentane,isopentane, n-octane, petroleum ether, methylcyclopentane, cyclohexaneor the like diluent from source 77 may be introduced by way of valvedline 78 into line 74.

In extractor 76 the oil is contacted with liquid sulfur dioxide and BFS.If desired the combined reagents may be introduced into the upperportion of tower 76 from storage drum 81 through line S2. Alternatively,liquid sulfur dioxide alone may be introduced through line 82 and BF3may be introduced into the extraction Zone from source 84 by way of line86 and manifold 37.

Contacting in extractor 76 is effected at a temperature of C. and at apressureA of about 50 p. s. i. g. The amount of liquid sulfur dioxideintroduced into extractor 76 is 70 percent by volume, based on thevolume of oil. The amount of BF3 is 2.5 mols per gram atom of sulfurcontained in the oil. Tower 76 may be operated rainaterich orextract-rich; the latter mode of operation is preferred. The contactingtime in extractor 76 is about 5 minutes.

The rainate phase is withdrawn from the upper end of extractor 76through line 88 into stripping tower S9 which is provided with internalreboiler 91. Stripper 89 may be unpacked or may optionally containbubble trays, packing materials or other fractionating devices.Relatively small amounts of liquid SO2 and B133 which have been occludedin the rainate are vaporized in stripper 89 and are withdrawn throughline 93 for reuse. Product oil is withdrawn through line 94 to storagenot shown.

Further treatment of the product oil may be desired,

for example, treatment with concentrated sulfuric acid l or withselective solvents, alkali treatment, clay treatment, water washing orother refining treatment. If diluent has been used, this may be removedby distillation.

The extract phase is withdrawn from the lower portion of extractor 76through line 96 for treatment to separate extract materials and thecomponents of the agent, respectively. Herein the extract phase ispassed from line 96 .into stripper 97 which is provided with internalreboiler 98. Stripper 97 is similar in construction to stripper $9. Theextract phase is subjected to a sufficiently high temperature instripper 97 to vaporize essentially its entire content of sulfur dioxideand BFa. Such temperatures fall within the range of about 50 C. to about250 C. Suicient pressure must be maintained in stripper 97 to preventvaporization of the lower boiling portions of the extract. The sulfurdioxide and BF3 are passed overhead from stripper 97 by way of line 101.

Stripped extract is withdrawn from stripper 97 and is passed to storagenot shown by way of line 102. A portion of the extract may be recycledby way of valved line y103 to a lower point of extractor 76 as a reffuxstream.

The SO2 Vand EP3 are passed from line 101 through valved line 106 andline 107 into purication zone 108. Here nonfcondensible gases, HzS, etc.are removed by means well known to the liquid SO2 extraction art. Thepurified SO2 and BF; are passed into line 109 where they meet thematerial from line 93 and the combined stream is passed by way ofcondenser 110 and line 111in storage drum 81.

Makeup SO2 from source 112 is passed by line 113 and makeup BFg fromsource 114 is passed by line `115 into storage drum 81.

When the stream in line 101 contains little or no H28, the purificationzone may be by-passed and the SO2 and EP3 passed by way of valved line116 directly to line 109.

It is desirable from time to time to dehydrate at least a portion of thestream passing through line 101. A part of this stream is passed by wayof valved line 11S into dehydrator 119 which is provided with internalreboiler 121. Dehydrated SO2 and BFg are withdrawn overhead through line122 and are passed by way of line 107 to purification zone 108. A liquidbottoms fraction comprising water, sulfur dioxide and B133 hydrates iswithdrawn from the lower portion of dehydrator 119 by way of line 123for discharge from the system.

The extract may be subjected to various rening operations. For example,it can be given a catalytic hydroning treatment, employing aconventional catalyst, e. g., cobalt molybdate, and conventionaloperating conditions. The extract is a surprisingly good feed to acatalytic cracking operation; a high yield of very high octane gasolineis obtained, which gasoline has the remarkably low sulfur content ofless than 0.1 weight percent.

Numerous pumps, valves, heat exchangers and other engineering detailshave been omitted from the SO2-EP3 operation in the interests ofsimplifying the description. Common engineering process expedients,particularly those which have heretofore been employed in processes ofrefining hydrocarbon oils with liquid sulfur dioxide will readilysuggest themselves to those skilled in the art; it is to beV understoodthat such engineering expedients are within the purview of the presentinvention.

The results obtainable with the process of this invention areillustrated by the following comparative experiments. The charging stockused in all the experiments below was a West Texas virgin heater oildistillate, characterized as follows:

API 40 Sulfur (total), wt. percent 0.62 Mercaptan Number 48.1 Color,Saybolt 16 Color, aged, ASaybolt 12 ASTM distillation, F.:

Initial 332 10% 390 50% 446 502 Max. 565

The aged color is a measure of the storage stability of an oil. The agedcolor is determined by exposing m1. of the oil to the atmosphere in anopen beaker for 20 hours at a temperature of 200 F. The color of the oilat the end of the exposure is the aged color.

The extraction procedure consisted of adding 375 ml. of liquid sulfurdioxide to 750 ml. of oil contained in a reactor provided with a coolingjacket and mechanical agitator. The temperature of the reactor contentswas maintained at 20 C. When used, 1.7 mois of EP3 per gram atom ofsulfur in the oil were metered into the reactor and the reactor wasclosed. At this point a pressure of from l0 to 100 p. s. i. g., duelargely to B173, prevailed in the reactor, but when agitation wasstarted, the pressure fell rapidly to about 0 p. s. i. g. Agitation wascontinued for 20 minutes at -20 C. followed by a 30-minute settlingperiod to furnish ample time for the extract and rafiinate phases toseparate. The extract phase was drawn oli at the bottom of the reactorand the rainate phase was washed with water and then with caustic.Finally the raffinate was again washed with water and dried.

Run 1 v In this run the feed was contacted with liquid SO2 alone. Theoil from the raflinate phase was sour to the doctor test. About one-halfof themercaptans has been removed by the extraction. A reverse doctortest indicated that the product oil contained no free-sulfur.

Run 2 In this run the feed was contacted with liquid SO2-BF3 agent. Theproduct oil wassweet to the doctor test. However, the reversedoctor testindicated that free-sulfur was present. y

y Run 3 v In this run the feed was contacted at 120 F. with a 50%aqueous KOH solution (2% based on feed) and air until the mercaptannumber of the oil had been reduced to 4.8. The Saybolt color of thesubstantially sweet oil was 4; the aged oil was a tan color falling inthe lower value of the ASTM-Union scale. No 'change had taken place inthe total sulfur content and the oil contained no free-sulfur. v

Run 4 The substantially `sweet oil fromv Run 3`Was treated with liquidSO2 alone. An 88V volume percent "yie1d of carried out in the presenceof a mercaptan oxidation catalyst.

5. The process of claim 1 wherein said mercaptan elimination processcomprises the doctor process.

6. The process of claim l wherein the mercaptan elimination processcomprises contacting said oil with a reagent solution comprising aqueouscaustic and methanol and separating a substantially mercaptan-free oilfrom a mercaptide-reagent solution phase.

' 7. The process of claim 1 wherein said promoter is product oil wasobtained. vThe product oil contained 0.36 weight percent sulfur(411%"reduction in sulfur content). The Saybolt color was 17 and theaged color was 9. The product oil was sour and contained no freesulfur.

Run 5 The substantially sweet oil from Run 3 was treated with liquidSO2- EP3 agent. An 86% yield of product 'poil was obtained.r The productoil contained 0.11 weight percent sulfur (82% lreduction in sulfurcontent).. The Saybolt color was 25 and the aged color was 2l; Theproduct oil was sweet and contained no free-sulfur.

These runs show that the presence of free-sulfur can be avoided if themercaptan containing oil is first rendered substantially doctor sweetprior to treatment With liquid SO2- EP3 agent. Further, the runs showthat a remarkable improvement in color stability is obtained by treatingan aqueous caustic-air sweetened oil with liquid SO2-EP3 agent ascompared with treating saidk oil with liquid SO2 alone.

Thus having described theinvention, what is claimed 1. A process forrefining a mercaptan-containing hydrocarbon oil, whichprocess comprises(1) treating said oil to substantially 'eliminate the mercaptanstherefrom, (2) contacting said substantially mercaptan-free oil with anagent consisting essentially of liquid SO2 and a promotor, wherein theliquid SO2 is present in an amount at least sufficient to form 4anextract phase and the promoter is selected from the class ofFriedel-Crafts metal halides consisting of A1C13, FeCla, TiCl4, BFs,HgClz, BC13 and ZnCl2 at a temperature below about |10 C., and (3)separating a rened rainate containing essentially no free-sulfur from anextract phase.

2. The process of claim whereinl said rnercaptanl 8. The process ofclaim 1 wherein said promoter is -9. The process of claim l wherein saidpromoter is FeCls.

10. A process for refining a hydrocarbon oil containing mercaptans andother organo-sulfur compounds, which process comprises l) treating saidhydrocarbon oil by aA process that produces a substantiallymercaptan-free and elemental sulfur-free oil, (2) contacting the oilfrom step (1) with an agent consisting essentially of liquid SO2, in anamount between about 15 and 200 volume percent based on oil, and apromoter selected from the class 'of Friedel-Crafts metal halidesconsisting of A1Cl3, FeCla, TiCLr, B133, HgCl2, BC13 and ZnC12, in anamount between about 0.5 and 5 mols per gram atom of sulfur in the oil,at a temperature between about 10 and 40 C., (3) separating a ranatephase from an extract phase, and (4) recovering a product oil markedlyreduced in organo-sulfur compound content and containing essentially nofree-sulfur as measured by the reverse doctor test from said raffinatephase.

11. The process of claim 10 wherein said hydrocarbon oil is a petroleumdistillate boiling in the heavierthan-gasoline range.

j 12. The process of claim 10 wherein said promoter is BFa and theBFs'is present in an amount between about 1 and 3 mols per gram atom ofsulfur in the oil.

13. The process of claim 10 wherein the oil from step (1) has amercaptannumber below about 5.

14. A process for refining a high organo-sulfur compound containing sourpetroleum distillates boiling in the heavier-than-gasoline range, whichprocess comprises (l) contacting said distillate with a catalytic amountof an aqueous caustic solution in the presence of freeoxygen underconditions to reduce the mercaptan numl ber of said distillate to belowabout 5, (2) separating distillate is a heater oil boiling between about330 and References Cited in the le of this patent UNITED STATES PATENTS1,941,251 Davis Dec. 26, 1933 2,451,025 Ellenden Oct. 12, 1948 2,534,025Howes et a1 Dec. 12, 1950 '2,560,330 Brandon July 10, 1951 2,626,893Morrow Ian. 27, 1953 2,646,390 Arnold et al July 21, 1953 2,671,046Arnold et a1. Mar. 2, 1954

1. A PROCESS FOR REFINING A MERCAPTAN-CONTAINING HYDROCARBON OIL, WHICHPROCESS COMPRISES (1) TREATING SAID OIL TO SUBSTANTIALLY ELIMINATE THEMERCAPTANS THEREFROM, (2) CONTACTING SAID SUBSTANTIALLY MERCAPTAN-FREEOIL WITH AN AGENT CONSISTING ESSENTIALLY OF LIQUID SO2 AND A PROMOTOR,WHEREIN THE LIQUID SO2 IS PRESENT IN AN AMOUNT AT LEAST SUFFICIENT TOFORM AN EXTRACT PHASE AND THE PROMOTOR IS SELECTED FROM THE CLASS OFFRIEDEL-CRAFTS METAL HALIDES CONSISTING OF ALCL3, FECL3, TICL4, BF3,HGCL2, BCL3 AND ZNCL2 AT A TEMPERATURE BELOW ABOUT